Ecc 3:14
I know that everything God does will remain forever; there is nothing to add to it and there is nothing to take from it, for God has so worked that men should fear Him.

Now, the next verse…

Ecc 3:15
That which is has been already and that which will be has already been, for God seeks what has passed by.

Read it again.

That which “is” has been already…the moment we think about “now” it becomes/is the past.
That which “will be” has already been from God’s perspective.

He created “time”.
He is not “locked-in” to any of His creation.
He is “outside”…without any created limit.
God in not bound by the linear flow of time.

Yesterday.
Today.
Tomorrow.
All are the same to God.
He knows all about each.

“God seeks what has passed by”?

Read some other translations.

Ecc 3:15
Whatever is, has already been, and whatever will be, already is. God repeats what has passed.
HSCB

Ecc 3:15
That which hath been is now; and that which is to be hath already been; and God requireth that which is past.
KJV

Ecc 3:15
That which is, already has been; that which is to be, already has been; and God seeks what has been driven away.
ESV

Ecc 3:15
That which is has already been,
And what is to be has already been;
And God requires an account of what is past.
NKJV

Ecc 3:15
Whatever is has already been, and what will be has been before; and God will call the past to account.
NIV

There will be an accounting.

Rejoice in the wonder and glory of the Most High.
Truly His ways are above us.